Tubular beam with center leg and method for forming the same

ABSTRACT

A reinforcement beam is roll formed from a metal sheet for use in a vehicle bumper system. The reinforcement beam includes adjacent tubes having a common center wall and lateral portions extending from opposing sides of the common center wall that are roll formed simultaneously in the same rotational direction to enclose interior volumes of the adjacent tubes and to define top and bottom walls and front and rear wall of the reinforcement beam. The front walls of the adjacent tubes each include a channel rib depressed into the interior volume of the respective adjacent tube longitudinally along the reinforcement beam for stiffening the respective front wall. A weld is formed separately in each of the seams between the front walls and between the rear walls, thereby defining a crevice rib between the channel ribs to improve the bending strength and torsional strength of the reinforcement beam.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/779,310, which was filed on Feb. 27, 2013, entitled “APPARATUS FORMAKING TUBULAR BEAM WITH CENTER LEG,” which is a divisional of U.S.patent application Ser. No. 13/228,920, which was filed on Sep. 9, 2011,entitled “TUBULAR BEAM WITH SINGLE CENTER LEG,” and are herebyincorporated by reference in their entirety. U.S. patent applicationSer. No. 13/228,920 claims benefit and priority of provisionalapplication Ser. No. 61/385,680, filed Sep. 23, 2010, entitled TUBULARBEAM WITH SINGLE CENTER LEG, the entire contents of which areincorporated herein by reference.

BACKGROUND

The present invention relates to bumper reinforcement beams used invehicle bumper systems, where the beam is tubular and has a single(mono) center leg. The present invention also relates to roll formingapparatus and methods of forming said beams. However, the presentinvention is not believed to be limited to only bumper reinforcementbeams for vehicles.

Modern vehicle bumper systems typically include a reinforcement beamdesigned for strength and impact characteristics in order to meetgovernment and insurance industry standards for particular vehicles, butalso designed to minimize overall vehicle weight, to maximizestrength-to-weight ratios, to fit within confined vehicle packagespaces, and to satisfy vehicle aesthetic and functional requirements atfront and rear ends of vehicles. Concurrently, the processes and methodsof manufacturing the beams preferably minimize undesired productdimensional and quality variations, while also minimizing manufacturingcost, optimizing manufacturability and minimizing scrap. Roll formingprocesses and methods have proved to be particularly effective atproducing high volume runs of bumper reinforcement beams withcompetitive cost and high dimensional consistency. However, the industryis very competitive, such that even small improvements can be important.

Further, many of the desired features above are conflicting, such thatit is not clear how to improve a particular bumper reinforcement beam,or how to improve the roll forming process for making the beam. Forexample, a heavier beam may be stronger, but would cause an unacceptableincrease in vehicle weight. High strength materials may be preferred,but they are expensive, difficult to form, and cause high wear ontooling. Accurate control over positioning of sheet edges during theroll forming process is desired to facilitate an accurate beamcross-sectional shape, to reduce tolerances along the edges so thatexcess material along the edges can be reduced in order to minimize beamweight, and to facilitate consistent contact during welding. However,this can require extra roll forming steps and stations as well asadditional tooling, hardware and software controls, each of whichincrease capital investment and make the roll forming process morecomplex. The above beams include two sheet edges formed against othermaterial of the sheet, with each being welded by a welder to permanentlyform the tubular shape of the beams. However, welders take up spacealong the roll form apparatus, especially where the welders arepositioned at different stations along a length of a roll formapparatus, thus increasing floor space requirements considerably, aswell as capital investment. Nonetheless, it is difficult to weld in twoopposing sides of a beam due to flying debris adversely affecting one orboth of the welders. Notably, welds must be consistent and reliable inorder to provide reliable and consistent impact strength in the bumperreinforcement beams and in the related bumper systems.

SUMMARY OF THE PRESENT INVENTION

In one aspect of the present invention, a reinforcement beam is rollformed from a metal sheet for use in a vehicle bumper system. Thereinforcement beam includes adjacent tubes having a common center walland lateral portions extending from opposing sides of the common centerwall that are roll formed simultaneously in the same rotationaldirection to enclose interior volumes of the adjacent tubes and todefine top and bottom walls and front and rear wall of the reinforcementbeam. The top and bottom walls are parallel with the common center walland the front and rear walls of the reinforcement beam are in coplanaralignment with each other and perpendicular with the common center wall.The front walls of the adjacent tubes each include a channel rib that isdefined by a portion of the respective front wall depressed into theinterior volume of the respective adjacent tube longitudinally along thereinforcement beam for stiffening the respective front wall. Seams aredefined between the front walls and between the rear walls by a bendradius being roll formed on lateral edges of the metal sheet to extendthe lateral edges into the interior volumes of the adjacent tubes inabutting and continuous contact with the common center wall. A weld isformed separately in each of the seams at a weld station that holds aconsistent rectangular cross section of the reinforcement beam in placeand the lateral edges against the common center wall, thereby defining acrevice rib between the channel ribs to improve the bending strength andtorsional strength of the reinforcement beam.

In another aspect of the present invention, a reinforcement beam is rollformed from a metal sheet for use in a vehicle bumper system. Thereinforcement beam includes adjacent tubes having a common center walland lateral portions extending from opposing sides of the common centerwall. The lateral portions are roll formed simultaneously in the samerotational direction to enclose interior volumes of the adjacent tubesand to define top and bottom walls of the reinforcement beam that areparallel with the common center wall and coplanar aligned front and rearwalls of the reinforcement beam that are perpendicular with the commoncenter wall. Seams are defined between the front walls and between therear walls by a bend radius being roll formed on lateral edges of themetal sheet to extend the lateral edges into the interior volumes of theadjacent tubes in abutting contact with common center wall. A weld isformed in each of the seams at a weld station that holds a consistentrectangular cross section of the reinforcement beam in place and thelateral edges against the common center wall. Also, a curved shape isformed in a plane parallel to the common center wall longitudinallyalong the reinforcement beam and adapted to correspond with anaerodynamic shape of a corresponding vehicle.

In yet another aspect of the present invention, a method is provided forforming a reinforcement beam from a metal sheet for use in a vehiclebumper system: The method includes roll forming a metal sheet to formadjacent tubes having a common center wall and lateral portionsextending from opposing sides of the common center wall. The lateralportions are roll formed simultaneously in the same rotational directionto enclose interior volumes of the adjacent tubes and to define top andbottom walls of the reinforcement beam that are parallel with the commoncenter wall and coplanar aligned front and rear walls of thereinforcement beam that are perpendicular with the common center wall.During the simultaneous roll forming of the lateral portions, the methodincludes forming the front walls of the adjacent tubes to each include achannel rib defined by a portion of the respective front wall thatprotrudes into the interior volume of the respective adjacent tube andextends longitudinally along the reinforcement beam for stiffening therespective front wall. The method also includes welding a continuousstrip of bonded material in a seam that is defined between the frontwalls by the common center wall abutting a bend radius formed on alateral edge of the metal sheet that extends the lateral edge into theinterior volume of the respective adjacent tube. Upon welding thecontinuous strip of bonded material in the seam, the seam defines acrevice rib between the channel ribs to stiffen the bending strength andtorsional strength of the reinforcement beam.

Related reinforcement beams and methods also form a part of the presentinvention.

These and other aspects, objects, and features of the present inventionwill be understood and appreciated by those skilled in the art uponstudying the following specification, claims, and appended drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a top view of a bumper reinforcement beam that is tubular andincludes a single center leg.

FIG. 2 is a cross-sectional view along line II-II in FIG. 1.

FIG. 3 is a view of the roll forming apparatus for performing thepresent roll forming process.

FIG. 4 is a series of cross sections labeled S1-S33 showing a shape ofthe original sheet at each forming step when forming the beam of FIG. 1.

FIG. 5 is a cross section of the beam in FIGS. 1-2 including seamtracking discs forming part of a weld station.

FIG. 6 is a modified beam similar to FIGS. 1-2 but having a modifiedcross section.

FIG. 7 is a side view showing a welding station near an end of the rollforming process.

FIG. 8 is a cross section through the welding station of FIG. 7, showinga pressure box fixture for holding the roll formed beam's final shapeduring a simultaneous double-weld step.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A bumper reinforcement beam 40 (FIG. 1) includes a tubular reinforcementbeam 50 for a vehicle bumper system, and mounts 41 attached to the beam50 to facilitate attachment to a vehicle frame, such as for use in afront bumper system (illustrated in FIG. 1) or rear bumper system of avehicle. The illustrated beam 50 includes a longitudinal center section42 curved at a first radius R1 and longitudinal outer ends curved at atighter second radius R2 in order to match an aerodynamic shape of aparticular vehicle. However, it is contemplated that the presentinventive concepts can be used on any beam, whether linear or swept, andwhether consistently curved/swept with a single radius or havingdifferent longitudinal curves (“sweeps”).

The present beam 50 is made of sheet steel material having a thicknessof 0.8 mm to 1.4 mm and a tensile strength of about 800 to 2000 MPa(i.e. about 120 to 290 ksi). The illustrated beam is about 80 mm highand 40 mm deep (in vehicle-mounted position), with two channel ribsbeing formed in the beam's front face (one over each tube). Eachillustrated channel rib is about 8-10 mm deep and 8-10 mm wide, andincludes a rounded bottom. However, it is contemplated that the presentbeam can be made of different materials, including AHSS (Advanced HighStrength Steels) and that it can be made from a sheet having a thicknessof about 0.8 mm-3.0 mm thick (or such as 0.8 mm to 1.4 mm thickness),and can be made in different beam cross-sectional sizes, such as about80 mm-150 mm high, and 30 mm-60 mm deep, and having a length equal to orslightly greater than a distance between vehicle mounts/bumper framerail tips.

The present beam 50 (FIG. 3) is formed from a single sheet of steelmetal on a roll forming apparatus via a series of paired rolls in rollforming stations, with each station performing a forming operation, suchas shown by the roll formed flower pattern of steps 1-33 in FIG. 4.During the process, a single sheet is formed to have adjacent tubesformed on opposite sides of a single center wall (sometimes called a“mono” wall or “center leg,” herein). The roll former includes a firstregion of forming rolls in stations S1-S7, including forming a centersection (i.e. the center wall) with outer sections of the sheetextending outwardly and generally perpendicular to the center wall.Radiused sheet edges are also formed in steps S1-S7. The roll formerfurther includes a second region of forming rolls in stations S8-S33forming first and second tubes on each side of the center leg andsharing the center leg as a common wall. The channel ribs aresubstantially formed in steps S8-S12, and help in controlling a lateralposition of the sheet as it traverses along the roll form apparatus.Laser welding occurs at or after station S33. Alternatively, the weldingcan occur in two separate steps, such as in a roll forming process wherethe first tube is formed halfway through the process (well before thelast forming station).

Specifically, as illustrated, slightly less than “half” of the sheet isdeformed in a first direction (illustrated as clockwise in FIG. 4) intoa first tube with a first radiused edge of the sheet abutted against aradiused end of the center wall (and welded), and an opposite “half” ofthe sheet is deformed in an opposite second direction (such ascounter-clockwise) into a second tube with a second radiused edgeabutted against the other radiused end of the center wall (and welded).The line of contact for welding on the first radiused edge is at an endof the radius where a terminal tip of the sheet becomes “flat.”Similarly, the line of contact of the radiused end of the center wall isat an end of the center wall where the center wall becomes “flat.”However, it is desirable to have the radius be the primary contact sothat the laser beam of the welding process has optimal conditions formaking a consistent weld. Notably, the welding process includes a laserbeam entering the crevice and heating material at the abutting linecontact formed by the radiused end and radiused edge. For this reason,it may be desirable that the terminal tips of the sheet edges be formedso that they do not cause a gap at the bottom of the crevice despiteprocess variations, which gap would (could) adversely affect welding,depending on a size of the gap.

Notably, the welding box fixture assists with setting the line contactand with setting a desired abutting pressure for the welding process atthe line contact. The mating materials are held abuttingly against eachother by the weld fixture shown in FIG. 8, as discussed below, tofacilitate a good weld. A radiused shape of the edges allows goodcontact, yet allows the edges to flex, slide, and bend (caused by forcesgenerated in the weld box fixture), especially along slip plans P1 andP2, allowing the fixture to “set” and maintain a desired cross-sectionalshape in the weld station. This arrangement facilitates good welding,and potentially decreases the criticality of perfect dimensionality ofthe edges. Concurrently, the edges of the sheet include a tip section ofmaterial inside the beam that extends away from the weld line. As notedabove, the free end of the tip section is necessary to assure that thereis sufficient material to weld despite material variations along theedge and process variations. However, excess material in the free end ofthe tip section results in waste and added weight to the bumper beam. Byaccurately controlling contact and engagement of the edges and abuttingmaterial, a length of the “free end” can be minimized, thus reducing anoverall weight of the beam to a minimum. It is noted that even ounces ofreduced weight can be important to automotive engineers and vehicledesigners. The illustrated “free end” is expected to be less than about4 mm, but it is contemplated that it potentially could be reduced suchas to 2 mm, depending on particular process parameters and functionalrequirements of the beam.

As noted, the radiused edges of the sheet advantageously facilitate andallow for consistent and forgiving abutting engagement as they extendinto contact with and are welded to mating radiused (bent) corners onthe center leg of the beam. The double radius of the edges and of thecenter leg ends allows the two sections of material to reliably engagein line contact and engage within a desired range of abutment force,thus better accommodating dimensional variations during themanufacturing process. This configuration facilitates good line contactof the abutting material sections and thus facilitates good weldingdespite dimensional and process variations. At the same time, theradiused edges and “free ends” of the edges are recessed into the frontand rear faces of the beam so that vertical planes defined by the frontand rear surfaces of the beam are not interrupted by anyoutwardly-protruding edge of the sheet, which can be important tomeeting vehicle manufacturer specifications. Also, the center leg isformed from a center of the sheet (and not from a side edge of thesheet). By forming the center leg first and by making it from a centerof the sheet, the roll form process is more balanced and controlled,making it easier to control a lateral position of the sheet. In otherwords, “wandering” of the sheet in the roll former is reduced due tofirst forming the center leg, since the center leg then acts as a“center anchor” during later forming of the sheet. This increasedaccurate positional control of the sheet results in the ability tofurther reduce tolerances of the “free end” of the edges, since a widetolerance is not required. It is contemplated that the “free ends” ofthe edges can be reduced to 4 mm or less, and even as low as 2 mm orless, depending on process controls and characteristics of the sheet androll forming process.

The tubular reinforcement beam 50 with center leg is particularly suitedfor use as a reinforcement beam in a vehicle bumper system due to itshigh strength-to-weight ratio, due to its resistance to longitudinalbending due to an impact inward of its ends, and due to its torsionalresistance to rotational forces such as from a vertically-off-centerimpact.

As noted above, the beam 50 (FIG. 2) is formed from a single unitarysheet in a continuous roll forming process (FIG. 6). The beam 50includes first and second edges 51 and 52 and seven wall sections 53-59extending sequentially therebetween. The first through fourth wallsections 53-56 form a first tube, and the fourth through seventh wallsections 56-59 form an adjacent second tube, with the wall section 56being a common shared wall. The wall sections 53-55 and 57-59 combine toform a tubular shape with a center leg formed by horizontally-extendingwall section 56 (when in a vehicle-mounted position), and with wallsections 55 and 59 forming a vertical coplanar front face and wallsections 53 and 57 forming a vertical coplanar rear face. The first edge51 is deformed to form a radius CR1 of about 3-4 mm, with its tip 51′(i.e. “free end” having a length of about 4 mm or potentially as smallas 2 mm) extending so that an inner surface 61 of the first edge 51 liesparallel the center wall section 56. The radius CR1 and associatedradiused corner 62 (formed by the fourth and fifth wall sections 56-57on the front face of the beam) engage and are welded to permanently setthe first tube.

In beam 50, the second edge 52 is also deformed inwardly to form aradius similar to radius CR1 (such as about 3-4 mm in the illustratedbeam), but with its terminal tip 52′ extending parallel the center wallsection 56. The radius CR1 engages and is welded to an associatedradiused corner 64 formed by the fourth and third wall sections 56 and55. The illustrated beam 50 has a cross section that is generallyrectangular, with a center leg dividing the rectangle into adjacentequal-sized first and second tubes. This cross section has been found toprovide excellent bending stiffness, torsional stiffness, and arelatively high strength-to-weight ratio.

The illustrated first wall section 53 includes a channel rib 65 (i.e. aninwardly formed depression, also sometimes called a “power rib”) thatfurther stiffens the wall section 53 and accordingly stiffens the frontface of the beam and stiffens the first tube section. The illustratedchannel rib 65 is generally centered along wall section 53 and has awidth diameter about 10%-40% of a width of the wall section 53 (or morepreferably about 20%-30% of the width) and has a depth about equal toits width diameter. The fifth wall section 57 also includes a channelrib 66 (similar in size, shape, and location to rib 65) that stiffensthe wall section 57, and accordingly stiffens the front face of the beamand the second tube section. The radii CR1 formed by the first edge 51and tip 51A and by the second edge 52 and tip 52A have center pointslocated inside the respective tubes formed thereby. The bottoms of theillustrated channel ribs are semicircularly shape. Nonetheless, it iscontemplated that a depth and size of the channel ribs can be madeshallow, deeper, wider, narrower, flat-bottomed, or otherwise modifiedto satisfy specific functional requirements of a beam.

Notably, the radiused shape of the edges 51 and 52 and mating cornerscause them to form a crevice rib that also stiffens the beam 50 and thusstabilizes the front and rear walls/faces of the beam 50 in a manner nottotally unlike the channel ribs 65 and 66. On the beam's front face, thecrevice rib formed by the radiused shape of front edge 51 and associatedcorner combine with the two channel ribs 65 to effectively form threeribs on a face of the beam 50, each stiffening the bending strength andtorsional strength of the beam. Testing has shown that a stiffness ofthe beam can be increased sufficiently to offset any additional materialweight added by virtue of the channel ribs requiring a wider sheet tomanufacture the beam. The crevice rib is generally aligned with thecenter wall, and the cavity it defines is about 3-4 times as deep as across-sectional thickness of the material of the sheet. Specifically,the cavity of the illustrated crevice rib is about 3-4 mm deep, based ona sheet material thickness of about 0.8 mm-1.2 mm. The laser weld islocated at a bottom of the crevice where the material first comes intoabutting contact.

It is contemplated that the welds 70 and 71 will be made using laserwelders 72 and 73 (FIG. 3). The present welders 72 and 73 are located ina single station S33, which provides significant advantages in terms ofspace utilization, wiring, and process control. The welds 70 and 71(FIG. 2) are formed at the outboard abutting material in the crevice,such that the welds are spaced slightly from the terminal ends (i.e. the“free ends”) of the first and second edges, such as about 4 mm, orpotentially down to about 2 mm. The illustrated curved abuttinginter-engagement of sheet material has been found to be forgiving andallows some dimensional variation and dimensional control within thewelding fixture without adversely affecting the line contact and thewelding operation. Even though the present welders 72 and 73 are locatedin a single station S33, it is contemplated that they could be locatedin separate stations along the roll former apparatus if desired or if aparticular application requires that.

Notably, the beam, including its cross-sectional profile and the welds70 and 71, are symmetrical. This greatly helps keep the beam uniform andstraight (and helps avoid snaking and non-linear bending due tonon-balanced weld heats and material shrinkage/movement) during rollforming and manufacturing operations. Persons skilled in the art of rollforming will recognize how balanced the forming process is in each ofthe steps S1-S33 (FIG. 4). In particular, persons skilled in the art ofroll forming manufacture and design will recognize the value of theperpendicularity of the center wall in step S7, and also the value ofthe perpendicularity of the outer walls in step S21, and theminimization of roll forming steps thereby facilitated.

The related method of manufacturing a tubular reinforcement beam 50 withcenter wall section 56 for a bumper reinforcement beam 40 (see the rollformer in FIG. 3, and the beam in FIGS. 1-2) includes steps of:providing a sheet 49 (see FIG. 3) including first and second edges 51-52(FIG. 2) and seven wall sections 53-59 extending sequentiallytherebetween; bending the center wall to a perpendicular orientation tothe remaining material (see steps S2-S7), bending the edge tips (stepsS3-S7) and forming the channel ribs 65, 66 (started in steps S3-S9 andfinishing the channel ribs in steps S10-S12), bending the first throughfourth wall sections 53-56 to form a first tube and bending the fourththrough seventh wall sections 56-59 to form an adjacent second tube(half formed in steps S3-S21 and finishing same in steps S22-S33);welding the first edge 51 to the associated radiused corner 62 andwelding the second edge 52 to the associated radiused corner 64 whilemaintaining an accurate cross-sectional shape of the continuous beam ina weld fixture (see FIGS. 7-8); deforming the continuous beam to alongitudinally curved (“swept”) shape in the sweeping station, andcutting off the beam segments to length in a cutoff station to formindividual bumper reinforcement beams.

Notably, the channel rib 65 in the first wall section 53 and channel rib66 in the fifth wall section 57 combine with the crevice at a center ofthe beam front (over the center wall) to provide a three channel ribformation on a face of the beam. This provides excellent torsional andbending strength in the beam, as noted above. In particular, testing hasshown that channels and ribs providing stability to a face of the beamcan improve impact strengths significantly and provide increasedconsistency of impact strength (and consistency of energy absorbingability) without increasing beam weight, which is an unexpected andsurprising result. The improvement in impact strength is attributed toseveral factors. For example, the present beam's weight is not increasedover a similar sized beam not having channel ribs, because the presentbeam uses a thinner sheet material while still providing a similar orimproved impact test result. Notably, thinner materials can tend tounpredictably/prematurely kink and catastrophically collapse due to thedynamics that occur during an impact against thin sheet material,potentially increasing variability and inconsistency of impact strengthsduring testing. However, the channel ribs and crevice rib in the frontof the present beam help stabilize the tubular structure of the beam,thus providing improved test results even when a thinner sheet materialis used. This improvement was not expected given the fact that thechannel ribs and crevice rib are in the face of the beam. Part of thereason it was not expected is because the face-located channel ribs andcrevice ribs cause some sheet material to be located inward closer to abending moment's centerline (rather than farther away from thecenterline). Notably, material located closer to a bending moment'scenterline contributes less to the beam's bending moment, thuspotentially reducing the bending moment of inertia for the beam.However, due to the dynamics of impacts, stability of beam walls can bevery important to beam impact performance. Also, some bumper testingcauses vertically unbalanced torsional forces (such as when a testimpactor device strikes a beam higher than its centerline).

A related apparatus 88 (FIG. 3) for manufacturing a tubularreinforcement beam 50 with center wall section 56 for a bumperreinforcement beam 40 comprises a roll mill 89 with in-line sweepstation 90 and cutoff 91. The roll mill 89 includes rolls constructed toform a sheet 49 including first and second edges 51-52 and seven wallsections 53-59 extending sequentially therebetween. The rolls include afirst region of roll forming stations 92 with sets of rolls positionedto form the center leg with outer wings of the sheet extending generallyperpendicularly from the center leg. The first region of the rollforming stations 92 also forms the radiused edges of the sheet. A secondregion of roll forming stations 92′ includes roll sets positioned andconfigured to bend the first through fourth wall sections 53-56 to forma first tube and to bend the fourth through seventh wall sections 56-59to form an adjacent second tube, with the single center leg being commonto both tubes. First and second welders 72 and 73 are positioned to weldthe first edge 51 to the associated inner surface of radiused corner 62,and to weld the second edge 52 to the associated radiused corner 64. Thefirst welder 72 is positioned above the beam, and the second welder 73is positioned below the beam with its laser beam oriented at an angle,as described below.

It is noted that the present apparatus can utilize a roll mill withhorizontal axes supporting forming rolls, or alternatively can utilize aroll mill with vertical axes supporting forming rolls. In the verticalaxis mill, the laser welders would potentially operate from opposingsides of the beam or partially above the beam. An advantage of avertical axis roll mill is that gravity can be used to cause debris anddirt to fall away from the welding sites, since the welder is positionedoff to a side and/or above the welding. In the horizontal axis rollmill, the lasers operate from top and bottom positions relative to thebeam. The bottom position of one of the welders potentially causes aproblem with falling debris, but this problem is solved by the presentinnovation as discussed below.

As shown by the illustrated version in FIGS. 3 and 4, the apparatus ispreferably constructed where both welds are made at a single stationwith the welding being done simultaneously. One welder 72 is positionedabove the welding location and a second welder 73 is positioned belowbut significantly upstream of (or downstream of) the weld location. Thebottom welder is positioned and shielded so that the welder is notdetrimentally affected by flying and falling debris. For example, theillustrated bottom welder is located upstream of the actual welding siteby 15 degrees from vertical. Also, if necessary (depending on a distanceof the laser beam generating device from the weld location), a shieldcan be used to physically shield the laser generating device from theweld. The illustrated shield is a physical barrier located so that itdoes not interfere with the laser beam (which defines a line), but sothat the laser generating apparatus is protected from falling debris(which tends to define an arc as the debris initially moves laterallyand then falls by gravity toward an end of its falling path). It iscontemplated that the shield will also include an air shield provided bya directed air stream. Notably, a focal length of a laser welder beamcan be up to 36 inches, and the laser beam could be any of severaldifferent types, such as gas (CO₂), solid state, fiber, or disc.

It is noted that in the steps shown in FIG. 4, the center leg isinitially formed from a center of the sheet to a perpendicularorientation relative to a horizontal plane (which extends along a linelevel of the roll former) in the first few steps S1-S7. This anchors thesheet and keeps the sheet centered in the roll forming process, thuseliminating (or greatly reducing) a tendency of the sheet to wander orslide laterally during the forming process. It is noted that, due to thehigh strength properties of the present sheet and due to its thicknessand width, large lateral forces are generated during the roll formingprocess. By first forming the center leg to a perpendicular state,control of the sheet's lateral position is much easier and is moreinherently controlled/controllable. Also, radii are formed into edges ofthe sheet in steps S1-S7. Thereafter, the adjacent tubes are formed onopposite sides of the common center leg. As a result in the presentprocess of FIG. 4, the number of roll forming steps can be reduced to asfew as 33 steps (see FIG. 4) even when forming a sheet having 290ksi+tensile strength, which is considered to be a dramatic andsurprising and unexpected improvement from known methods. Notably, fewerforming steps can be very beneficial, since the reduced number of stepscan reduce tooling costs (i.e. fewer forming rolls necessary), reduce alength of the roll form apparatus (i.e. fewer roll form stations), andreduce overall processing time (i.e. a shorter cycle time from theinitial flat sheet to the double tube beam shape).

FIG. 5 illustrates a seam tracking disc 90′ used to track and controlthe crevice 80. (In FIG. 5, the disc 90′ is exploded away, but it iscontemplated that the disc will physically engage the beam 50 and trackalong the crevice.) The disc 90′ tracks a valley of the crevice 80 tofacilitate the welding process. Specifically, the disc 90′ is a rotatingdisc, resembling a pizza cutter, that rides inside the area for thecontinuous weld seam. The laser welder locates off of this disc in theweld valley. As illustrated, a disc 90′ can be used to track crevices atboth the top and bottom of the beam 50.

FIG. 6 is a cross section of the modified beam 50A similar to FIG. 2 butwith the tubes having different widths. Specifically, one tube of beam50A is about twice a width of the other tube. However, they share acommon center wall. Further, they both have a channel rib of similarsize and shape, and also there is a crevice rib formed over the centerleg. In the beam 50A, similar and identical features, characteristics,and components are identified by using identical numbers but with aletter (such as “A”). This is done to reduce redundant discussion. Itwill be understood by persons skilled in the art of bumper reinforcementbeams and related manufacturing processes that the beam 50A can and doesincorporate many features of beam 50, such that an individual discussionof numbers in beam 50A is not believed to be necessary.

FIGS. 3, 7-8 show a welding station 100 at an end of and as exiting aroll former. In FIG. 7, the sheet is shown as already having been formedin a roll former, and is traveling in a direction of travel D1. A weldbox fixture 102 is positioned in line with the partially-formed beam 50.Top and bottom laser welders 103 are positioned at the welding stationin a location where the weld box fixture will not interfere with theirrespective laser beams striking targeted abutting material of the beam50. The bottom laser welder 103 is positioned slightly upstream of theweld box fixture 102, and its welding laser 104 is oriented at adownstream angle so that the welding laser beam 104 strikes the beam 101at a desired location to heat and weld abutting material of the beam101. The laser has a focal length of up to 36 inches, depending on thetype of laser. There is no minimum distance of the laser from the weldlocation on the beam 101. For example, it is contemplated that the lasertype could be gas (such as CO₂), or could be solid state, fiber, or disclaser types. A maximum angle A1 of the laser 104 to the reinforcementbeam 101 is about 15 degrees from vertical (i.e. from perpendicular to aside of the beam 50). A physical shield 105 is used, if necessary ordesirable, to shield the laser source 106 from debris from the weldingprocess. The physical shield 105 can be downstream air knives or airjets, or can include a physical panel.

The adjustable weld box fixture 102 (FIG. 8) is located at the weldingstation and is designed for setting and holding a final shape of theroll formed beam during the welding step. The illustrated adjustablefixture 102 includes an external steel box frame 110, top and bottomexternal mandrels 111, 112, and adjustable side external mandrels 113,114 that are inwardly-pressured by actuators 115, 116. It iscontemplated that the actuators can be dynamic or active (such ashydraulic cylinders), or they can be adjustable and passive, such asthreaded bolts that can be adjusted to provide a desired amount ofinward pressure to maintain a desired shape of the external mandrelswithin the weld box fixture 102. Two rods are shown extending from theactuator 115 through the frame 110 to a location where they are attachedto the external mandrel 111. However, it is contemplated thatalternative connected and motivating arrangements can be constructed.

Internal mandrels 117, 118 are located in each of the tubes 121, 122 ofthe double tube beam 120, and are anchored by cables 123, 124 thatextend to an upstream anchor stanchion 125 located on the roll formerwhere the sheet is laterally open sufficiently to position the anchoringstanchion 125 (FIG. 3) for holding the cables 123, 124 (FIG. 8). Beam 50is illustrated, but it is contemplated that the beam could be like beam50A or another modified beam. The illustrated internal mandrels 117, 118each are split mandrels with opposing mandrel halves 126, 127 biasedapart by a spring 128 (e.g. hydraulic, mechanical, or other spring).Internal mandrel 118 also includes opposing mandrel halves 130, 131biased apart by hydraulic spring 132. However, it is contemplated thatin some circumstances, a one-piece solid internal mandrel can be used oneach side. A laser access opening is provided in the fixture box frame110 and external mandrels 111,112, with the illustrated laser accessopening 129 providing access for the laser beam through a bottom and topof the box frame 110 and through the top and bottom external mandrels111, 112.

The internal springs 128 and 132 and split internal mandrels 117, 118 incombination with the inward-biasing actuators 115, 116 and externalmandrels 113, 114 cause the fixture to maintain a desired outer shape ofthe beam 101 as it passes through the weld station 100 and is welded.Notably, there is a slip plane P1 defined between the top externalmandrel 111 and a top of the side external mandrels 113, 114. Also,there is a slip plane P2 defined between the bottom external mandrel 112and a bottom of the side external mandrels 113, 114. The slip plane P1aligns with the front face of the beam 101 and is defined in part by theoutboard surface of the tip of the front radiused end of the center leg,and the slip plane P2 aligns with a rear face of the beam 101 and isdefined in part by the outboard surface of the tip of the rear radiusedend of the center leg. In the welding station, pressure from theinternal and external mandrels of the welding fixture cause sheetmaterial to move and deform to an accurate known position along the slipplanes P1 and P2. This improves dimensional consistency and accuracy ofa cross-sectional shape of the beam prior to (and during) the weldingprocess. Also, by this arrangement, the pressure on the abuttingsurfaces where the welds will occur can be more accurately andconsistently controlled for an optimal weld condition.

It is to be understood that variations and modifications can be made onthe aforementioned structure without departing from the concepts of thepresent invention, and further it is to be understood that such conceptsare intended to be covered by the following claims unless these claimsby their language expressly state otherwise.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A reinforcement beamroll formed from a metal sheet, said reinforcement beam comprising: abumper reinforcement beam for a vehicle that includes adjacent tubeshaving a metal sheet shaped to include a common center wall and lateralportions of the metal sheet extending from opposing sides of the commoncenter wall that enclose interior volumes of the adjacent tubes todefine top and bottom walls of the bumper reinforcement beam that areparallel with the common center wall and front and rear walls of thebumper reinforcement beam that are in coplanar alignment with each otherand perpendicular to the common center wall; wherein the adjacent tubeseach include a channel rib that is defined by a portion of therespective front wall depressed into the interior volume of therespective adjacent tube longitudinally along the bumper reinforcementbeam for stiffening the respective portion of the front wall; whereinseams are defined between the adjacent tubes along the front wall andalong the rear wall, and wherein the seams are formed by a bend radiusof about 3-9 mm that is roll formed at edge portions of the lateralportions of the metal sheet with a tip of each of the edge portions inabutting and continuous contact with the common center wall; and a weldformed separately in each of the seams on the front and rear walls ofthe bumper reinforcement beam, wherein the welds are configured to beformed by welders of a weld station that holds a consistent rectangularcross section of the bumper reinforcement beam in place and that holdslateral edges of the metal sheet against the common center wall tosubstantially close the seams when forming the welds, wherein a rearcrevice rib having the bend radius of one of the edge portions isdefined by the weld along the seam on the rear wall, and wherein a frontcrevice rib having the bend radius of the other of the edge portions isdefined by the weld along the seam on the front wall between the channelribs, and wherein the front and rear crevice ribs are generally alignedwith the common center wall to improve bending strength and torsionalstrength of the bumper reinforcement beam.
 2. The reinforcement beam ofclaim 1, wherein the welds each include a continuous strip of bondedmaterial formed by laser welding.
 3. The reinforcement beam of claim 1,wherein the adjacent tubes are longitudinally curved along at least apart of their length in a plane parallel to the common center wall forconforming with an aerodynamic shape of a vehicle bumper.
 4. Thereinforcement beam of claim 1, wherein the channel ribs are generallycentered over a front surface of the respective tube and formed inparallel alignment with the front crevice rib.
 5. The reinforcement beamof claim 1, wherein the channel ribs are roll formed during simultaneousbending of the lateral portions and protrude into the interior volume adepth at least two times a thickness of the metal sheet.
 6. Thereinforcement beam of claim 1, wherein the bend radius is of about 3-4mm, and wherein radiused corners are defined between the common centerwall and the lateral portions to substantially minor the bend radius atthe edge portions of the metal sheet, thereby defining sides of theseams opposite the edge portions.
 7. The reinforcement beam of claim 1,wherein the metal sheet has a material thickness of less than 1.2 mm. 8.The reinforcement beam of claim 1, wherein the metal sheet has a tensilestrength of greater than 250 ksi.
 9. A vehicle reinforcement beam rollformed from a metal sheet for use in a vehicle bumper system, saidvehicle reinforcement beam comprising: a bumper reinforcement beam for avehicle that includes adjacent tubes having a metal sheet shaped toinclude a common center wall and lateral portions extending fromopposing sides of the common center wall and curved to enclose interiorvolumes of the adjacent tubes and to define top and bottom walls of thebumper reinforcement beam that are parallel with the common center walland front and rear walls of the bumper reinforcement beam that areperpendicular to the common center wall; wherein seams are disposedbetween the adjacent tubes along the front wall and along the rear wall,and wherein the seams are formed by a bend radius of about 3-9 mm thatis roll formed at edge portions of the lateral portions of the metalsheet with a tip of each of the edge portions abutting the common centerwall; a weld formed in each of the seams at the front and rear walls ofthe bumper reinforcement beam, wherein the welds are configured to beformed by welders of a weld station that holds a consistent rectangularcross section of the bumper reinforcement beam in place and the edgeportions against the common center wall to substantially close the seamswhen forming the welds; wherein a rear crevice rib having the bendradius of one of the edge portions is provided by the weld along theseam on the rear wall, and wherein a front crevice rib having the bendradius of the other of the edge portions is provided by the weld alongthe seam on the front wall between channel ribs formed on a portion ofthe respective front wall, and wherein the front and rear crevice ribsare generally aligned with the common center wall to improve bendingstrength and torsional strength of the bumper reinforcement beam; andwherein the front and rear walls have a curved shape extendinglongitudinally along the bumper reinforcement beam and adapted tocorrespond with an aerodynamic shape of a corresponding vehicle.
 10. Thevehicle reinforcement beam of claim 9, wherein the welds each include acontinuous strip of bonded material formed by laser welding.
 11. Thevehicle reinforcement beam of claim 9, wherein the adjacent tubes eachinclude one of the channel ribs that protrudes into the interior volumeof the respective adjacent tube and extends longitudinally along thebumper reinforcement beam for stiffening the front wall.
 12. The vehiclereinforcement beam of claim 11, wherein the channel ribs are generallycentered over a front surface of the respective adjacent tube and formedin parallel alignment with the crevice rib.
 13. The vehiclereinforcement beam of claim 12, wherein the channel ribs are roll formedduring simultaneous bending of the lateral portions and protrude intothe interior volume a depth at least two times a thickness of the metalsheet.
 14. The vehicle reinforcement beam of claim 9, wherein radiusedcorners are defined between the common center wall and the lateralportions at a location where the edge portions come into abuttingcontact with the common center wall, and wherein the radiused cornerssubstantially mirror the bend radius on the edge portions, therebydefining sides of the seams opposite the edge portions.
 15. The vehiclereinforcement beam of claim 9, wherein the metal sheet has a materialthickness of less than 1.2 mm and a tensile strength of greater than 250ksi.